Range finder for finding range by image realization

ABSTRACT

A range-finder, capable of finding a range by image realization, having two distantly arranged imaging devices. The first pattern having a predetermined size and the first positional information is extracted by the pattern extracting section from the first image of a target which has been made by the first imaging device. In the second image of the same target, which has been made by the second imaging device, the second pattern having the second positional information, which is most correlated with the first pattern in a plurality of upward and downward horizontal or vertical lines corresponding to the first positional information, is detected by the correlation processing section. Parallax is found from the first and the second positional information by the parallax calculating section. A distance to the target is found from this parallax by using the principle of triangulation.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority of Japanese Patent Application No.2001-186779, filed on Jun. 20, 2001.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a range finder used for supporting adriver when the driver drives an automobile. More particularly, thepresent invention relates to a range finder for finding a range to atarget, which is running in front, by image realization, when aplurality of cameras or image pickup elements are used.

2. Description of the Related Art

In order to enhance the convenience and safety of driving an automobile,a driver support system has been recently put into practical use. Inthis driver support system, range finding to find a range to a vehiclerunning in front is one of the factors to be provided. A range to avehicle running in front has been detected until now by a range findingsystem, in which the range is found by image realization withcompound-eye cameras.

In the above conventional range finding system in which compound-eyecameras are used, a range to a vehicle running in front is found asfollows. A vehicle running in front is photographed by two cameras,which are mounted at a predetermined interval on a vehicle runningbehind, or by image pickup elements such as image sensors. The parallaxof the same object (the vehicle running in front) on the thus obtainedtwo images is utilized, and a range to the vehicle running in front isfound from this parallax by the principle of triangulation.

On the other hand, in some cases, distortion is caused on an imageobtained by each camera when the optical system is distorted. When theobtained image is distorted, it impossible to accurately calculate theparallax, and range finding is erroneously conducted. In order to solvethe above problems, a distorted image photographed by each camera iscorrected by a distortion correcting circuit so that the distorted imagecan be processed to an image having no distortion, and then a range to atarget is found.

However, in the above conventional range finding method, as the entireimage photographed by each camera must be corrected, it becomesnecessary to provide a large-scale distortion correcting circuit and amemory to be incorporated into the distortion correcting circuit.Further, since the entire image must be corrected, a quantity ofprocessing necessary for correction is increased, which causes a drop inthe processing speed. Furthermore, even if the distortion is corrected,a fluctuation is caused in the pixel values of the images photographedby the right and left cameras. Therefore, it is difficult to accuratelycalculate the parallax. Furthermore, the above conventional rangefinding is disadvantageous in that a road surface (shadows, white linesand characters on the road) becomes an object of range finding in somecases.

SUMMARY OF THE INVENTION

The present invention has been accomplished to solve the above problemsof the conventional range finding method for finding a range to a targetby image realization. It is an object of the present invention toprovide a range finder capable of finding a range to a target at highspeed without having an error in range-finding caused by distortion ofan image without providing a large-scale correcting circuit and memory.

It is another object of the present invention to provide a range findercapable of accurately finding a range to a target by correcting afluctuation caused between images photographed by a right and a leftcamera.

It is still another object of the present invention to provide a rangefinder capable of accurately finding a range to a target without havingan error in range-finding caused by a road surface.

In order to solve the above problem, the present invention provides arange finder for finding a range to a target by image realizationcomprising: a first and a second imaging device arranged at apredetermined interval; a pattern extracting section for extracting afirst pattern having a predetermined size and the first positionalinformation from a first image of the target which has been made by thefirst imaging device; a correlation processing section for detecting asecond pattern having the second positional information, which is mostcorrelated with the first pattern, from a plurality of horizontal orvertical lines located at positions corresponding to the firstpositional information in the second image of the target which has beenmade by the second imaging device; and a parallax calculating sectionfor finding parallax from the first and the second positionalinformation. When a correlation is found by a plurality of upward anddownward lines, it is possible to accurately find parallax withoutconducting correction with respect to the distortion and axialmisalignment.

In a range finder of the present invention, the correlation processingsection finds a correlation with the first pattern for every a pluralityof horizontal or vertical lines, and the second pattern having thesecond positional information, which is most correlated with the firstpattern, is detected according to the plurality of pieces of correlationwhich have been found. A correlation is found by a plurality of upwardand downward lines, and when it is judged how far a correlating positionon each line departs from a vertical line, a pattern can be accuratelyrealized even if other confusing patterns exist.

In a range finder of the present invention, it is preferable that thefirst image is divided into a proximity region, which can be easilycorrelated, and a background region which is difficult to be correlated,and the correlation processing section finds a correlation with thefirst pattern for every a plurality of horizontal or vertical lines onlywhen the first pattern exists in the background region. In thisconstitution, only when the pattern is realized in a background regionin which it is difficult to correlate, a correlation is found by aplurality of upward and downward lines.

It is preferable that a range finder of the present invention furthercomprises an image correcting section for detecting a state ofmisalignment of the first or the second image according to thecorrelation of the first pattern with the second pattern for every aplurality of horizontal or vertical lines which has been found by thecorrelation processing section, and for correcting the first or thesecond image according to the state of the detected misalignment.

Further, it is preferable that a range finder of the present inventionfurther comprises an alarm generating section for generating an alarmwhen a value of correlation, which is obtained in the case where thecorrelation processing section detects the second pattern, is comparedwith a correlation reference value and when the value of correlation isnot more than a correlation reference value. When the distortion of animage plane and the misalignment of an axis are large and it isimpossible to accurately conduct range finding, an alarm is generated.

In order to solve the above problems, a range finder for finding a rangeto a target by image realization of the present invention comprises: afirst and a second imaging device arranged at a predetermined interval;a density difference detecting section for finding a density differencebetween the first image and the second image from the first image of thetarget, which has been made by the first imaging device, and the secondimage of the target which has been made by the second imaging device; animage density correcting section for correcting density of the first orthe second image according to the density difference between the firstand the second image; a pattern extracting section for extracting afirst pattern having a predetermined size and first positionalinformation from the first image; a correlation processing section fordetecting a second pattern having the second positional information,which is most correlated with the first pattern, in the second image ofthe target which has been made by the second imaging device; and aparallax calculating section for finding parallax from the first and thesecond positional information. When a difference of density between theright and the left image is found and one of the images is corrected byutilizing the difference in density, it becomes possible to accuratelyconduct range finding.

In order to solve the above problems, a range finder for finding a rangeto a target by image realization of the present invention comprises: afirst and a second imaging device arranged at a predetermined interval;a density difference detecting section for finding a density differencebetween the first image and the second image from the first image of thetarget, which has been made by the first imaging device, and the secondimage of the target which has been made by the second imaging device; apattern extracting section for extracting a first pattern having apredetermined size and first positional information from a first image;an image density correcting section for correcting density of the firstpattern according to the density difference between the first and thesecond image; a correlation processing section for detecting a secondpattern having the second positional information which is mostcorrelated with the corrected first pattern in the second image; and aparallax calculating section for finding parallax from the first and thesecond positional information. When a difference of density between theright and the left image is found and only the pattern is corrected byutilizing the difference of density, it becomes possible to accuratelyconduct range finding.

It is preferable that a range finder of the present invention furthercomprises a parameter setting section for setting a parameter necessaryfor processing conducted by the correlation processing section accordingto a density difference between the first and the second image. When theparameter necessary for correlation processing is changed by thedifference of density found from the right and the left image, rangefinding can be more accurately conducted.

In order to solve the above problems, a range finder for finding a rangeto a target by image realization of the present invention comprises: afirst and a second imaging device arranged at a predetermined interval;a pattern extracting section for extracting a first pattern having thefirst positional information containing a range finding target from thefirst image of the target which has been made by the first imagingdevice; a correlation processing section for detecting a second patternhaving the second positional information, which is most correlated withthe first pattern in the second image of the target which has been madeby the second imaging device; a parallax calculating section for findingparallax from the first and the second positional information; a rangefinding section for finding a range to the range finding target by theparallax; a realizing section for realizing a height of the rangefinding target according to the position in the first or the secondimage of the range finding target and according to the result of rangefinding conducted by the range finding section; and a nullifying sectionfor nullifying the result of range finding conducted by the rangefinding section in the case where the height of the range finding targetis smaller than the reference height. The height of the range findingtarget is realized by the position in the image, the range of which wasfound, and by the result of range finding. When the height is not morethan a predetermined height from the ground, the target of range findingis realized as characters and shadows on a road, and the result of rangefinding is nullified.

It is preferable that a range finder of the present invention furthercomprises a road surface position correcting section for detecting awhite line in the first or the second image and for finding a range to aforward end portion of the white line and for correcting a road faceposition, which becomes a reference to realize the height of the rangefinding target, from the value of range finding of the forward endportion of the white line. When the position of the ground in the imageis corrected by the result of realization of a white line on a road, itbecomes possible to judge a height agreeing with the road environment.

A range finder of the present invention further comprises a road surfacecorrecting section for detecting a third pattern having the samecharacteristic as that of the white line from the first or the secondimage and for finding a range to the forward end portion of the thirdpattern and for correcting a road face position, which becomes areference to realize the height of the range finding target, from thevalue of range finding of the forward end portion of the third pattern.Another pattern such as a character on a road surface having the samecharacteristic as that of a white line on the road surface is extractedfrom an image, and its forward end portion is used as a reference andthe position of the ground in the image is corrected. Due to theforegoing, it becomes possible to judge a height agreeing with the roadenvironment.

In a range finder of the present invention, it is preferable that thereference value correcting section corrects a reference value accordingto a plurality of range finding values of the forward end portion of thethird pattern. The reference value is corrected according to data sentfrom a plurality of positions.

Further, in a range finder of the present invention, it is preferablethat the reference value correcting section corrects the road surfaceposition by utilizing only a range finding value in a predeterminedrange of values in the plurality of range finding values of the forwardend portion of the third pattern. Without using data outside thepredetermined range of values, the reference value is more accuratelycorrected.

In order to solve the above problems, a range finder for finding a rangeto a target by image realization of the present invention comprises: afirst and a second imaging device arranged at a predetermined interval;a pattern extracting section for extracting a first pattern having apredetermined size and the first positional information containing therange finding target from the first image of the target which has beenmade by the first imaging device; a correlation processing section fordetecting a second pattern having the second positional information,which is most correlated with the first pattern in the second image ofthe target which has been made by the second imaging device; a parallaxcalculating section for finding parallax from the first and the secondpositional information; a range finding section for finding a range tothe range finding target by the parallax; a judging section for judgingwhether or not the range finding target exists in a range findingobjective region according to the result of range finding to find arange to the target and also according to the position of the rangefinding target in the first or the second image; and a nullifyingsection for nullifying the result of range finding conducted by therange finding section in the case where the range finding target existsoutside the range finding objective region. When range finding isconducted only in a predetermined range, the processing time of rangefinding can be reduced.

A range finder further comprises a height realizing section forrealizing a height of the range finding target according to the positionof the range finding target in the first or the second image, whereinthe nullifying section does not nullify the result of range findingconducted by the range finding section in the case where the height islarger than a predetermined reference value of the height even if therange finding target exists outside the objective region of rangefinding. In the case where the height is a predetermined value althoughit is outside the range finding objective region, it becomes possible tomore accurately realize a range finding target when it is made to be arange finding object.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be more clearly understood from thedescription as set forth below with reference to the accompanyingdrawings, wherein

FIG. 1A is a view for explaining the principle of a conventional rangefinding system in which compound-eye cameras are used;

FIG. 1B is a view showing images photographed by a right and a leftcamera shown in FIG. 1A for explaining the principle of parallax rangefinding;

FIG. 1C is a view showing an image containing distortion made by acamera and also showing an image obtained when the image distortion hasbeen corrected by a distortion correcting circuit;

FIG. 2A is a block diagram showing an outline of the constitution of arange finder of an embodiment of the present invention;

FIG. 2B is a block diagram showing an outline of the constitution of arange finder of another embodiment of the present invention;

FIG. 3A is a view showing a left input image photographed by a leftcamera and also showing a first pattern in the image;

FIG. 3B is a view showing a right input image photographed by a rightcamera, a graph of correlated values and a second pattern which is mostcorrelated with the first pattern in FIG. 3A extracted by thecorrelation processing;

FIG. 4 is a view for explaining the classification of an input imageinto a background region and proximity region;

FIG. 5 is a view showing an actual input image and a relation in which aroad surface position of the input image is shown, wherein the actualinput image and the relation are shown standing side by side;

FIG. 6 is a view for explaining a correction of a relation showing aroad surface position, wherein four correcting positions in an inputimage and a relation showing a road surface position of the input imageafter correction are shown standing side by side; and

FIG. 7 is a flow chart for explaining a correction procedure of arelation showing a road surface position.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Before describing the preferred embodiments, an explanation will begiven to the conventional range finder for finding a range by imagerealization shown in FIGS. 1A to 1C.

In the conventional range finding system for finding a range by imagerealization, range finding is conducted by using compound eye cameras.Referring to FIG. 1A, explanations will be made into a case in which adistance from a vehicle, which is running behind, to a vehicle 100,which is running in front, is found by the conventional range findingsystem using compound eye cameras. As shown in FIG. 1A, the left camera801 and the right camera 800 are horizontally arranged in the vehicle,which is running behind, at a predetermined interval (=base line length)B. The optical axis of the left camera 801 and that of the right camera800 are horizontally arranged. In this case, the same object in theimage photographed by the left camera 801 and that in the imagephotographed by the right camera 800 are shifted from each other inhorizontally. This misalignment between the position of the imagephotographed by the left camera 801 and that of the image photographedby the right camera 800 is referred to as parallax. The distance fromthe vehicle which is running behind to the vehicle which is running infront, can be found by the principle of triangulation in which thisparallax is utilized.

The image 901 shown in FIG. 1B is an example of the image photographedby the left camera, and the image 902 shown in FIG. 1B is an example ofthe image photographed by the right camera. Distance D (m) to a vehiclerunning in front can be found by the following expression.

D=f·B/{F(xb−xa)}

In this connection, (xb−xa) expresses parallax 903. In the aboveexpression, the left end of each image photographed by each camera isused as a reference, the lateral coordinate to a reference position ofthe image 901 photographed by the left camera is xb, the lateralcoordinate to a reference position of the image 902 photographed by theright camera is xa, the focal distance of each camera is f, the pixelpitch in each image is F, and the length of a base line is B.

In some cases, there is a possibility that distortion is caused in theimage photographed by each camera due to distortion in the opticalsystem. Distortion is high especially when a wide angle lens is used forthe camera. When distortion is caused in an image, it becomes impossibleto accurately calculate parallax, which causes an error in rangefinding. In order to solve the above problems, as shown in FIG. 1C, theentire image 1001 photographed by each camera containing distortion isprocessed into the image 1002 having no distortion by the distortioncorrecting circuit 1003, and then the aforementioned parallax (parallax903 shown in FIG. 1B) is calculated.

However, the above conventional method of range finding has thefollowing disadvantages. According to the above conventional method ofrange finding, as the entire image photographed by each camera must becorrected, it is necessary to provide a large-scale distortioncorrecting circuit and a memory used for the distortion correctingcircuit. Since the entire image must be corrected, a quantity ofprocessing of image data is increased, which causes a drop of theprocessing speed. Further, even if the distortion is corrected,fluctuation is caused in the pixel values of the images photographed bythe right and the left camera. Accordingly, it is difficult toaccurately calculate parallax. Furthermore, when range finding isconducted, a road face, on which shadows, white lines and charactersexist, becomes an object of range finding.

FIG. 2A is a block diagram showing an outline of the constitution of anembodiment of the range finder 10 of the present invention. The rangefinder 10, which is mounted on a vehicle, includes a left camera 11,right camera 12 and image processing section 13. Various signals areinputted from the range finder 10 into the driver support device 40mounted on the vehicle. According to the signals sent from the rangefinder 10, the driver support device 40 realizes a target such as avehicle, which is running in front, and an object existing ahead.According to the realization of the target and others, the driversupport device 40 helps evade a danger and warns a driver.

The image processing section 13 includes: a left image memory 21, rightimage memory 22, density difference detecting section 23, parametersetting section 24, image correcting section 25, pattern extractingsection 26, correlation processing section 27, parallax calculatingsection 28, range finding section 29 and diagnosis section 30.

The left camera 11 and the right camera 12 are respectively arranged atpositions in a vehicle (referred to as a self-vehicle hereinafter) onwhich the range finder 10 is mounted and at the same height from theground and at a predetermined interval so that parallax can be generatedin the visual field of each camera with respect to an object in thefield of view. The left camera 11 takes a photograph of space in thefield of view of the left camera 11. Data of the left image photographedby the left camera 11 are stored in the left image memory 21. In thesame manner, the right camera 12 takes a photograph of space in thefield of view of the right camera 12. Data of the right imagephotographed by the right camera 12 are stored in the right image memory22.

The left image 300 shown in FIG. 3A is an example of the left imagephotographed by the left camera 11, and the right image 310 shown inFIG. 3B is an example of the right image photographed by the rightcamera 12. In the left image 300 and the right image 310, referencenumeral 100 is a vehicle running in front, and reference numeral 101 isa white line on a road. In this embodiment, each image is composed of640 pixels existing in the direction of the x-axis and 480 pixelsexisting in the directions of the y-axis in the drawing. Each pixel hasdensity of 256 gradations.

The density difference calculating section 23 calculates average imagedensity of the inputted right and left images. Further, the densitydifference calculating section 23 calculates a difference in densitybetween the right and the left image. The thus calculated densitydifference data are sent to the image correcting section 25 and thediagnosis section 30.

The image correcting section 25 receives density difference data fromthe density difference calculating section 23 and corrects density ofthe entire left image according to the density difference data. That is,if a density difference is caused between the images inputted from theright and left cameras, it becomes impossible to accurately conduct thepattern matching which will be described later. Accordingly, there is apossibility that parallax cannot be accurately calculated and, further,range finding cannot be accurately conducted. For the above reasons, adensity balance between the right and left images is corrected. In thisconnection, density of the entire left image may not be corrected, anddensity may be corrected only in a specific region in the image whichhas been previously determined or detected.

In the case where a density difference received by the diagnosis section30 is higher than a predetermined value, the diagnosis section 30 judgesthat one of the right and left cameras or both of the right and leftcameras are defective. Then, the diagnosis section 30 sends an alarmsignal to the driver support device 40.

The pattern extracting section 26 extracts the first pattern 301 havingthe coordinate data (x1, y1)) from the left image 300. It is preferablethat the first pattern 301 is composed of 3×3 pixels or 4×4 pixels. Itis preferable that the first pattern 301 is extracted from an edgesection of the range finding target (the vehicle 100 in the case of theleft image 300) by means of edge detection.

The correlation processing section 27 detects the second pattern, whichis most correlated with the first pattern 301 in the left image 300extracted by the pattern extracting section 26, from the right pattern310 by means of pattern matching, so that the coordinate data of thesecond pattern can be detected. Pattern matching of the first pattern301 with the right image 310 is conducted on the five upward anddownward lines (the lines 311 to 315 in FIG. 3B) round the y-coordinate(y1) of the first pattern 301, that is, pattern matching of the firstpattern 301 with the right image 310 is conducted among the five pixelsin the direction of the y-axis. It is preferable that pattern matchingis conducted among the five upward and downward lines. However, it ispossible to adopt the other numbers of lines if necessary. Further, arange on the x-axis on which pattern matching is conducted can bepreviously set in the range from xm to xn round the x-coordinate (x1) ofthe first pattern 301. In this connection, in this embodiment, patternmatching is conducted on a plurality of upward and downward lines in thedirection of the y-axis, however, pattern matching may be conducted on aplurality of upward and downward lines in the direction of the x-axis.

According to the conventional method, after distortion of the right andleft images or misalignment of the axis has been corrected, patternmatching is conducted. However, in this embodiment, such a correction isnot conducted but pattern matching is conducted on a plurality of upwardand downward lines in the direction of the y-axis or the x-axis.According to this embodiment, as described above, even if a correctionof distortion is not conducted on the inputted right and left images, itbecomes possible to accurately find parallax when a plurality of lines,which are located upward and downward, are correlated. Accordingly, itbecomes unnecessary to provide a large-scale correcting circuit andmemory for correcting distortion on the entire image plane. Further, thesecond pattern can be detected without requiring the processing time forcorrecting distortion on the entire image plane.

Pattern matching is conducted as follows. First, on each line on they-axis, a window of the same size as that of the first pattern 301 isset for each pixel on the x-axis, and a value of correlation of eachwindow with the first pattern 301 is calculated. Further, the value ofcorrelation of each window is plotted on a graph, and a window, thevalue of correlation of which is highest, is realized as the secondpattern which is most correlated with the first pattern 301. In thisconnection, a value of correlation is found by calculation in which awell known cross correlation function is used. As an example of the wellknown cross correlation function, there is provided a method of SSDA(Sequential Similarity Detecting Algorithm) in which ∫∫|f—t| dxdy isused as a scale of matching.

FIG. 3B is a graph 320 showing values of correlation. Graphs 321 to 325shown in the graph 320 of values of correlation respectively correspondto the lines 311 to 315 of the right image 310. According to the rightimage 320, it can be judged that the highest correlation can be obtainedat the coordinate x2 on the x-axis in the graph 323. Accordingly, it canbe judged that the second pattern, which is most correlated with thefirst pattern 301 in the right image 310, is a pattern indicated by thereference numeral 331 in the right image 330 after the completion ofprocessing of correlation, and the coordinate is (x2, y2)). In thisconnection, in the graph 320 of the values of correlation, all graphshave a peak value at the coordinate x2. Therefore, even if the graph 325has a peak value at the coordinate x3, the coordinate except for x2 canbe excluded. That is, it is possible to prevent the occurrence of anerror of range finding in a state of a plurality of graphs (a state ofdistribution of values of correlation).

In this connection, the parameter setting section 24 can conductprocessing of correlation in the correlation processing section 27 andsetting of various parameters relating to the pattern extracting section26 according to a density difference between the right and the leftimage calculated by the density difference calculating section 23. Forexample, it is preferable that a threshold value for extracting an edgeused in the pattern extracting section 26 and a threshold value forjudging a correlation coincidence used in the correlation processingsection 27 are set according to the density difference. In thisconnection, since a value of correlation becomes low when the densitydifference is small, when the threshold value of the value ofcorrelation is lowered according to the density difference, it becomespossible to accurately judge a coincidence of correlation.

The parallax calculating section 28 finds parallax of the range findingtarget (vehicle) 100 from the coordinate (x1, y1)) of the first pattern301 in the left image 300 shown in FIG. 3A and the coordinate (x2, y2))of the second pattern 331 in the right image 330 shown in FIG. 3B. Inthis case, parallax can be expressed by the following expression.

Parallax=((x2−x1)²+(y2−y1)²)^(1/2)

The range finding section 29 finds a range between the range findingtarget 100 and the self-vehicle according to parallax calculated by theparallax calculating section 28 and sends the thus obtained range datato the driver support device 40. In this way, data of the distance tothe range finding target can be sent to the driver support device 40. Inthe above example, data of range finding are found in one portion in theimage, however, data of range finding may be simultaneously found for aplurality of portions in the image. Alternatively, data of range findingmay be found in a plurality of portions of the range finding target andan average value may be found from a plurality of data, so that theaverage value can be used as data of range finding of the range findingtarget 100.

In FIG. 2A, the left image memory 21 and the right image memory 22 canbe respectively realized by the frame memories. The density differencecalculating section 23, parameter setting section 24, image correctingsection 25, pattern extracting section 26, correlation processingsection 27, parallax calculating section 28, range finding section 29and diagnosis section 30 may be respectively realized by a differentprocessing circuit. Alternatively, they may be realized when programsfor conducting calculation of the processing sections are successivelyexecuted in a computer having a CPU and various memories.

In the range finder 10 shown in FIG. 2A, for example, sampling isconducted once in several seconds on the y-coordinate of the secondpattern 331, which is most correlated in the right image 330 in FIG. 3B,so that the misalignment of y-coordinate can be detected. Positions ofthe five upward and downward lines, on which correlation proceeding isconducted, may be corrected by utilizing the thus detected misalignment.The misalignment of the axes of the right and left images can becorrected by this correction.

FIG. 2B is a block diagram showing an outline of another range finder 10of the present invention. Like reference characters are used to indicatelike parts in FIGS. 2A and 2B. Different points of the range findershown in FIG. 2B from that shown in FIG. 2A are described as follows. Inthe range finder shown in FIG. 2B, after the first pattern 301 has beenextracted from the input image, which was photographed by the leftcamera 11, by the pattern extracting section 26, only the thus extractedfirst pattern 301 is corrected in the pattern correcting section 31 byusing the density difference data calculated by the density differencecalculating section 23. In the range finder shown in FIG. 2B, the entireimage or the image in a specific region is not corrected like the rangefinder shown in FIG. 2A, and the density of only the extracted patternis corrected. Therefore, the processing time can be shortened. The otherpoints of operation of the range finder shown in FIG. 2B are the same asthose of the range finder 10 shown in FIG. 2A. Therefore, furtherdetailed explanations will be omitted here.

Next, referring to FIG. 4, operation of the correlation processingsection 27 will be explained below. As shown in FIG. 4, the correlationprocessing section 27 divides an inputted image into two regions of thebackground region 401 and the proximity region 402 by the boundary line400, and the range finding method is changed for each region. Only whenthe first pattern extracted by the pattern extracting section 26 existsin the background region 401, correlation processing is conducted on thefive upward and downward lines. When the first pattern extracted by thepattern extracting section 26 exists in the proximity region 402,another simple correlation processing is conducted. The reason is that,in general, correlation processing can be easily conducted in theproximity region 402, however, correlation processing cannot be easilyconducted in the background region 401. In this connection, a positionof the boundary line 400 is appropriately determined according to thesystem. Concerning the simple correlation processing, it is possible toconsider to conduct pattern matching on the same coordinate as they-coordinate of the first pattern.

Next, a procedure of realizing the height of the range finding target100 will be explained below referring to FIG. 5. Reference numeral 500shown in FIG. 5 is a graph showing a relation between the y-coordinatein the inputted image and distance D from the right 12 and the leftcamera 11. In this case, a curve shown by reference numeral 502 is arelation showing a road surface position of the inputted image, and acurve shown by reference numeral 501 is a relation showing apredetermined height (reference value, for example 20 cm) from the roadface. In the input image 510 shown in FIG. 5, the line 511 shows a roadsurface position corresponding to the relation 501. Then, in the graph500 shown in FIG. 5, the region 503 corresponds to an object, the heightof which is not less than the reference value of height from the roadsurface position.

Accordingly, when the graph 500 shown in FIG. 5 is utilized, it ispossible to judge whether or not the height of the range finding targetis not less than the reference value of height by the position(y-coordinate) in the inputted image of the range finding target and bythe result of range finding (D). The realization of height of the rangefinding target may be conducted by the height realizing meansindependently provided in the image processing section 13 or by therange finding section 29.

Only when the height of the range finding target is not less than thereference value of height (in the case corresponding to the region 503),the result is made valid. When the range finding target corresponds tothe other regions, it is judged that it is not a range finding targetsuch as a road face, white line, road face character or object, and theresult of range finding is made invalid. The above invalid processing ofthe result of range finding may be conducted by the height invalid meansindependently arranged in the image processing section 13.Alternatively, the above invalid processing of the result of rangefinding may be conducted by the range finding section 29.

Next, referring to FIGS. 6 and 7, correction of a relation showing aroad surface position will be explained below. In the same manner asthat of the graph 500 shown in FIG. 5, the graph 600 shown in FIG. 6shows a position (y-coordinate) in the inputted image and shows distanceD from the left 11 and the right camera 12. A curve shown by referencenumerals 601 is a relation showing a previously set road surfaceposition. However, the road surface position variously changes accordingto the vibration of a vehicle and the environmental condition of theroad. Therefore, it is preferable that the relation showing the roadsurface position is corrected by the inputted image.

Referring to FIG. 7, a procedure of correcting the relation showing theroad surface position will be explained as follows. In the step 701,first, a position of the white line (the white line 101 of the image 610in FIG. 6) on the road face is realized from the input image, and thecoordinate is extracted. At this time, the range finding portion P issimultaneously designated. For example, it is preferable that P=4portions.

Next, in step 702, range finding is conducted in one portion (forexample, a portion shown by reference numeral 611 in the image 610) ofthe forward end portion of the realized white line. Next, in step 703,it is judged whether or not a position of the range finding result istoo close to a previously set range. In the case where the position ofthe range finding result is not too close to the previously set range,in step 704, it is judged whether or not the position of the rangefinding result is too distant from the previously set range. In the casewhere the position of the range finding result in step 704 is not toodistant from the previously set range, the program proceeds to step 705,and it is judged that the range finding result is valid. On the otherhand, in the case where it is judged that the position of the rangefinding result is excessively close to the previously set range in step703, and in the case where it is judged that the position of the rangefinding result is excessively distant from the previously set range instep 704, it is judged in step 706 that the result of range finding isinvalid. Therefore, the result of range finding is not used forcorrection.

In the next step 707, it is judged whether or not the number ofportions, which have been judged to be valid, is larger than P which hasbeen set in step 701. When the number of portions, which have beenjudged to be valid, is not more than P which has been set in step 701,the procedures in steps 702 to 706 are repeated again. For example, inthe image 610 shown in FIG. 6, range finding is conducted in fourportions of the points 611 to 614.

On the other hand, in the case where it is judged in step 707 that thenumber of portions, which have been judged to be valid, is larger thanP, the program proceeds to step 708. By utilizing the results of rangefinding conducted at the range finding portions, the number of which islarger than P, a correction value for correcting the relation 601showing a road surface position is calculated. In the successive step709, the relation 601 showing the road surface position is corrected. Byutilizing the results of range finding conducted in a plurality ofportions, it becomes possible to correct the relation 601 to therelation 602 more accurately showing the road surface position.Specifically, it is preferable that the correction is conducted asfollows. An average of the ratios (B/A) of the distance (A) beforecorrection at four points of 611 to 614, at which range finding has beenconducted, to the range finding value (B) obtained by range finding isfound, and the relation 601 showing the road surface position iscorrected to the relation 602 showing a new road surface position by theaverage.

For example, concerning the distance (A) at four points beforecorrection, the graph 600 shown in FIG. 6 is found by the y-coordinateof each point and the relation 601, and the distance (A) is 20 m at thepoint 611, the distance (A) is 5 m at the point 612, the distance (A) is20 m at the point 613 and the distance (A) is 5 m at the point 614.Concerning the range finding values (B) at four points, when the rangefinding value (B) is 22 m at the point 611, the range finding value (B)is 6 m at the point 612, the range finding value (B) is 22 m at thepoint 613 and the range finding value (B) is 6 m at the point 614, anaverage of the ratios (B/A) is 1.125 m. Therefore, it is possible tofind a new relation 602 in which the correction is conducted for 1.125m.

Since the relation 602 showing a road surface position has beencorrected, the relation 605 showing a position higher than the referencevalue of height from the road surface position is corrected according tothe correction of the relation 602, and the range 604 in whichcorrelation processing is conducted is changed in step 710. In this way,a series of procedure can be completed.

The above procedure shown in FIG. 7 may be conducted by a road surfacecorrecting means independently provided in the image processing section13. Alternatively, the above procedure shown in FIG. 7 may be conductedby the range finding section 29. In the above example, the road surfaceposition is corrected by using a white line on a road surface.Alternatively, it is possible to correct the relation showing the roadface position by utilizing a pattern on the inputted image plane, thecolor of which is white and the length in the direction of the y-axis ofwhich is somewhat large. An example of the aforementioned pattern ischaracters drawn on the road face.

It is preferable that the correction range of the relation showing aroad surface position is in a predetermined range (a range of the graph603 in the graph 600 shown in FIG. 6, for example, in a range of ratios(B/A) 0.8 to 1.2).

When the range 604, in which correlation is conducted, changed in step710 is utilized and correlation processing is conducted only on therange finding target corresponding to the range, a period of time inwhich correlation processing is conducted can be reduced. Therefore, therange finding time can be greatly reduced and the occurrence of an errorin range finding can be prevented.

As described above, according to the present invention, it isunnecessary to provide a large-scale correction circuit and memory forconducting distortion correction of an inputted image. Accordingly, thesize and cost of the range finder can be reduced.

According to the present invention, it is possible to accurately conductrange finding of a target without conducting distortion correction on aninputted image.

Further, when a road surface position is corrected according to thepresent invention, it becomes unnecessary to conduct range finding on anunnecessary target. Therefore, range finding can be accurately conductedat high speed.

What is claimed is:
 1. A range finder for finding a range to a target byimage realization comprising: a first and a second imaging devicearranged at a predetermined interval; a pattern extracting section forextracting a first pattern having a predetermined size and firstpositional information from a first image of the target which has beenmade by the first imaging device, wherein the first image is dividedinto a proximity region, which can be easily correlated, and abackground region which is difficult to be correlated; a correlationprocessing section for detecting a second pattern having secondpositional information, which is most correlated with the first pattern,from a plurality of horizontal or vertical lines located at positionscorresponding to the first positional information in the second imagingdevice wherein the second pattern having the second positionalinformation, which is most correlated with the first pattern, isdetected according to the plurality of pieces of correlation which havebeen found and wherein the correlation processing section finds acorrelation with the first pattern for the plurality of horizontal orvertical lines only when the first pattern exists in the backgroundregion; and a parallax calculating section for finding parallax from thefirst and the second positional information.
 2. A range finder accordingto claim 1, further comprising: an image correcting section fordetecting a state of a misalignment of the first or the second imageaccording to the correlation of the first pattern with the secondpattern for a plurality of horizontal or vertical lines which has beenfound by the correlation processing section, and for correcting thefirst or the second image according to the state of detectedmisalignment.
 3. A range finder according to claim 1, furthercomprising: an alarm generating section for generating an alarm when avalue of correlation, which is obtained in the case where thecorrelation processing section detects the second pattern, is comparedwith a correlation reference value and when the value of correlation isnot more than a correlation reference value.
 4. A range finder forfinding a range to a target by image realization comprising: a first anda second imaging device arranged at a predetermined interval; a densitydifference detecting section for finding a density difference between afirst image of the target made by the first imaging device and a secondimage of the target made by the second imaging device; an image densitycorrecting section for correcting density of the first or the secondimage according to the density difference between the first and thesecond images; a pattern extracting section for extracting a firstpattern having a predetermined size and first positional informationfrom the first image; a correlation processing section for detecting asecond pattern having second positional information, which is mostcorrelated with the first pattern, in the second image of the target;and a parallax calculating section for finding parallax from the firstand the second positional information.
 5. A range finder according toclaim 4, further comprising: a parameter setting section for setting aparameter necessary for processing conducted by the correlationprocessing section according to a density difference between the firstand the second image.
 6. A range finder for finding a range to a targetby image realization comprising: a first and a second imaging devicearranged at a predetermined interval; a density difference detectingsection for finding a density difference between a fist image of thetarget made by the first imaging device and a second image of the targetmade by the second imaging device; a pattern extracting section forextracting a first pattern having a predetermined size and firstpositional information from the first image; an image density correctingsection for correcting density of the first pattern according to adensity difference between the first and the second images; acorrelation processing section for detecting a second pattern havingsecond positional information which is most correlated with thecorrected first pattern in the second image; and a parallax calculatingsection for finding parallax from the first and the second positionalinformation.
 7. A range finder for finding a range to a target by imagerealization comprising: a first and a second imaging device arranged ata predetermined interval; a pattern extracting section for extracting afirst pattern having first positional information containing a rangefinding target from a first image of the target which has been made bythe first imaging device; a correlation processing section for detectinga second pattern having second positional information, which is mostcorrelated with the first pattern in a second image of the target whichhas been made by the second imaging device; a parallax calculatingsection for finding parallax from the first and the second positionalinformation; a range finding section for finding a range to the rangefinding target by the parallax; a realizing section for realizing aheight of the range finding target according to the position in thefirst or the second image of the range finding target and according toresult of range finding conducted by the range finding section; and anullifying section for nullifying the result of range finding conductedby the range finding section in the case where the height of the rangefinding target is smaller than the reference height.
 8. A range finderaccording to claim 7, further comprising: a road surface positioncorrecting section for detecting a white line in the first or the secondimage and for finding a range to a forward end portion of the white lineand for correcting a road face position, which becomes a reference torealize the height of the range finding target, from the value of rangefinding of the forward end portion of the white line.
 9. A range finderaccording to claim 7, further comprising: a road surface correctingsection for detecting a third pattern having same characteristic as thatof a white line from the first or the second image and for finding arange to a forward end portion of the third pattern and for correcting aroad face position, which becomes a reference to realize the height ofthe range finding target, from the value of range finding of the forwardend portion of the third pattern.
 10. A range finder according to claim9, wherein the reference value correcting section corrects the referencevalue according to a plurality of range finding values of the forwardend portion of the third pattern.
 11. A range finder according to claim10, wherein the reference value correcting section corrects the roadsurface position by utilizing only a range finding value in apredetermined range of values in the plurality of range finding valuesof the forward end portion of the third pattern.
 12. A range finder forfinding a range to a target by image realization comprising: a first anda second imaging device arranged at a predetermined interval; a patternextracting section for extracting a first pattern having a predeterminedsize and first positional information containing the range findingtarget from a first image of the target which has been made by the firstimaging device; a correlation processing section for detecting a secondpattern having second positional information, which is most correlatedwith the first pattern, in a second image of the target which has beenmade by the second imaging device; a parallax calculating section forfinding parallax from the first and the second positional information; arange finding section for finding a range to the range finding target bythe parallax; a judging section for judging whether or not the rangefinding target exists in a range finding objective region according tothe result of range finding to find a range to the target and alsoaccording to the position of the range finding target in the first orthe second image; and a nullifying section for nullifying the result ofrange finding conducted by the range finding section when the rangefinding target exists outside the range finding objective region.
 13. Arange finder according to claim 12, further comprising: a heightrealizing section for realizing a height of the range finding target,wherein the nullifying (section does not nullify the result of rangefinding conducted by the range finding section when the height is largerthan a predetermined reference value of the height even if the rangefinding target exists outside the objective region of range finding.